In recent years, as a projection video apparatus capable of performing large-screen display, various projection display apparatuses (projectors) using an optical modulation device have been attracting attention. These projection display apparatuses use light emitted from a light source serving as light generating means to illuminate a liquid crystal of a transmission type or a reflection type or an optical modulation device, which can perform optical modulation, such as a DMD (digital micro-mirror device) which can change a reflection direction with micro-mirrors arranged in array, form an optical image, which corresponds to a video signal supplied from the outside of the optical modulation device, on the optical modulation device, and enlarge and project the optical image, which is illumination light modulated by the optical modulation device, on a screen with a projection lens.
Examples of an important optical characteristic of a large screen projected in this way include brightness and uniformity of the brightness. It is important to condense light, which is generated from a lamp serving as a light source, on an optical modulation device serving as a light-receiving surface and illuminate the optical modulation device with light beams having little unevenness of brightness. It has been strongly requested to improve efficiency of an illumination device of illuminating the optical modulation device and make brightness uniform.
In order to meet such a request, for example, an illumination device, which has a lens array constituted by irregular-shaped aperture lenses, has been proposed. FIG. 9 shows a structure of the illumination device. Beams of light emitted by a lamp 101 provided in a parabolic mirror 102 are divided by a first lens array 110 in which lenses having substantially the same shaped aperture are arranged two-dimensionally. Thereafter, the light reaches a light-receiving surface 106 via a second lens array 112 which has lenses of the same number as the divided light beams, that is, the same number as the lenses of the first lens array 110. In other words, the second lens array 112 is arranged such that the light beams, which have reached thereto from a predetermined lens of the first lens array 110, pass through a corresponding lens on the second lens array 112 to reach the light-receiving surface 106 (effective area). The divided light beams reach the light-receiving surface 106 and are superimposed one on top of another.
For example, FIG. 9 shows a state in which light passing through a second lens from the above of the first lens array 110 passes through a second lens from the above of the second lens array 112, which is in a correspondence relation with the lens of the first lens array 110, and is irradiated on the light-receiving surface 106. The respective light beams divided by the first lens array 110 pass through respective lenses of the second lens array 112, which are in a correspondence relation with the lenses of the first lens array 110, and are superimposed one on top of another on the light-receiving surface 106. Thus, even if a distribution of luminance of light emitted from the lamp 101 is uneven, uniform brightness can be obtained on the light-receiving surface 106.
In addition, at this point, light substantially parallel with an optical axis made incident on the first lens array 110 is condensed by the respective lenses in the first lens array 110 and forms light source images on the corresponding respective lenses of the second lens array. At this point, due to optical characteristics of the light source and the parabolic mirror, light close to an optical axis 7 is focused as a relatively large image, and light distant from the optical axis 7 is focused as a relatively small image on the second lens array 112. Therefore, as shown in FIG. 9, on the second lens array 112, lenses with a large aperture are arranged in the central part close to the optical axis, and lenses with a small aperture are arranged in the peripheral part distant from the optical axis. Consequently, the lens array constituted by the irregular-shaped aperture lenses as described above is adopted as the second lens array 112, whereby improvement of efficiency of the illumination device can be realized.
In the above-described method, in order to further improve efficiency, an arrangement of the light source images formed on the second lens array 112 is changed by adjusting (decentering) positions of center of curvature of the respective lenses in the first lens array 110. For example, in order to eliminate overlapping of light sources images in the vicinity of the optical axis, the positions of center of curvature of the respective lenses in the first lens array 110 are adjusted such that large useless spaces are eliminated by increasing spaces among the light source images in the vicinity of the optical axis and decreasing spaces among the light source images in the peripheral part. In addition, on the second lens array 112, light overflowing from the apertures can be reduced by, for example, increasing sizes the apertures through which light beams in the vicinity of the optical axis are passed while keeping sizes of the apertures through which light beams in the peripheral part are passed. Higher efficiency of use of light could be obtained by optimizing a shape of the second lens array such that the respective lenses in the second lens array 112 include the respective light source images in this way (e.g., see Japanese Patent Laid-Open No. 05-346557). FIG. 10 shows an example of an image which is formed on the second lens array 112 obtained as described above.
In addition, as shown in FIG. 11, there is also an illumination system with which high efficiency can be obtained by using plural light sources (e.g., see Japanese Patent Laid-Open No. 2000-171901). In this case, the second lens array 112 is not formed in an optimal shape as described in Japanese Patent Laid-Open No. 05-346557, but a second lens array (with apertures of the same shape) having substantially the same shape as the first lens array 110 is used.
Also, in a constitution described in Japanese Patent Laid-Open No. 2000-171901, and in a constitution in which a method of synthesizing plural light sources described in Japanese Patent Laid-Open No. 2000-171901 is applied to a constitution described in Japanese Patent Laid-Open No. 05-346557, as in the case in which the single light source is used, light source images formed in the central part of the lens array 112 are light source images which are large compared with light source images formed in the peripheral part. This phenomenon will be hereinafter described with reference to FIG. 11.
Since an ellipsoidal mirror 2 has a focusing action like a lens, light beams irradiated from a light-emitting portion 16 of a first focus 15 are condensed in the vicinity of a second focus 17 to form an image of the light-emitting portion 16 on the second focus 17 side on a prism 4. However, an action of the ellipsoidal mirror 2 is different from an action of a lens in the following point. That is, if a lens is used instead of using the ellipsoidal mirror 2, in the case of the lens, a ratio of a distance from a position of the light-emitting portion 16 to a lens surface having the focusing action and a distance from the lens surface to a position, where an image is focused, is always fixed whichever position of the lens light passes On the other hand, in the case in which the ellipsoidal mirror 2 is used, if a distance from the first focus 15, where the light-emitting portion 16 of the lamp 1 is arranged, to a reflection surface of the ellipsoidal mirror 2 having the focusing action is short, a distance from a position of the reflection surface to a second focus 17, where a light source image is formed, is long. In such a case, a relatively large light source image is formed on the second focus 17 side on the prism 4. Conversely, as the distance from the first focus 15 to the reflection surface of the ellipsoidal mirror 2 becomes longer, the distance from the reflection surface of the ellipsoidal mirror 2 to the second focus 17 becomes shorter. In such a case, a relatively small light source image is formed on the second focus 17 side.
Therefore, in the optical system shown in FIG. 11, when a light beam irradiated from the light-emitting portion 16 of the lamp 1 is reflected in the vicinity of the optical axis of the ellipsoidal mirror 2, the distance from the reflection surface of the ellipsoidal mirror 2 to the second focus 17 side on the prism 4 becomes relatively long. As indicated by a single arrow in FIG. 11, a light beam made incident on a synthesis mirror 6 of the prism 4 through such a path has a large outgoing angle and is made incident in the vicinity of an optical axis of a lens 8. As a result, this light beam passes through a lens 109 in the vicinity of the optical axis 7 of the first lens array 110 and focuses a relatively large light source image on a lens 111 in the central part of the second lens array 112.
On the other hand, when a light beam irradiated from the light-emitting portion 16 of the lamp 1 is reflected in a position distant from the optical axis of the ellipsoidal mirror 2, the distance from the reflection surface of the ellipsoidal mirror 2 to the second focus 17 side on the prism 4 becomes relatively short. As indicated by a double arrow in FIG. 11, the light beam made incident on the synthesis mirror 6 of the prism 4 through such a path has a small outgoing angle and is made incident in a position distant from the optical axis of the lens 8. As a result, this light beam passes through the lens 109 distant from the optical axis of the first lens array 110 and focuses a relatively small light source image on the lens 111 in the peripheral part of the second lens array 112. Note that the above description is true for a lamp 1′ and an ellipsoidal mirror 2′.
In this way, on the second lens array 112, relatively large two light source images are formed in the central part and relatively small two light source images are formed in the peripheral part. In addition, since a size of the light source image is different in the central part and the peripheral part, there is almost no space or there is a small space between two light source images on the second lens array 112 in the central part, but a relatively large space is formed in the peripheral part. FIG. 12 shows an example of a light source image on the second lens array formed as described above. FIG. 12 shows an example in which there are thirty-six lenses 9, there are two light sources, and seventy-two light source images are formed on the lens array 12.
In the illumination optical system using the first lens array 110 and the second lens array 112, only in the case in which a light source image condensed in the respective lenses 109 has passed through the apertures of the corresponding respective lenses 111 of the second lens array 112, the light source image is irradiated on an area, which should be illuminated, as an effective light beam. Therefore, in order to increase light beams which are irradiated on an area which should be illuminated, as in the case of the single light source, it is conceivable to increase a size of the apertures of the respective lenses 111 in the central part of the second lens array 112.
In addition, in another optical system, in the case in which an optical system of separating two polarized components inherent in natural light is arranged between the first lens array 110 and the second lens array 112 even if one light source is used, or in an optical system of making two optical axis substantially agree with each other by the time when light beams reach the second lens array 112 after the light beams are emitted from two light sources and reach the separate lens arrays 110, compared with the number of lenses NLA1 included in the first lens array 110, the number of lenses NLA2 included in the second lens array 112 is made equal to a number found by multiplying the number of light beams from one light source, which is divided by a polarized component or a wavelength band, or the number of light source N=2 by the number of lenses NLA1 of the first lens array as indicated by the following expression,NLA2=2×NLA1  (Expression 1)whereby an illumination device using plural light beams or light sources is constituted (e.g., see Japanese Patent Laid-Open No. 11-66926 and Japanese Patent No. 3301951).
However, when plural light sources are provided and the second lens array is provided with regular-shaped apertures or irregular-shaped apertures, since a gap exists between a pair of light source images formed on lenses in the peripheral part of the second lens array 112, there is a problem in that further improvement of efficiency cannot be attained. In this case, if a light source image, which is formed by a lens separate from the predetermined lens 109 of the first lens array 110, is arranged in the gap between this pair of light source images, since a light beam of a light source image, which is formed by the separate lens 109′, inserted between the pair of light source images is not condensed in an area which should be illuminated from the second lens array, after all, efficiency of use of the illumination device is declined.
This will be hereinafter described specifically. FIG. 13 shows an arrangement of images of two light sources on the second lens array 112 in the case in which irregular-shaped aperture lenses are used as the second lens array 112. As it is evident from FIG. 13, compared with light source images in the central part, light source images in the peripheral part of the second lens array are small images with spaces formed among the images.
FIG. 14(a) shows paths of light beams passing through the first lens array 110 and the second lens array 112 to reach the light-receiving surface 114 in the case in which irregular-shaped aperture lenses are used as the second lens array 112. Light having passed through a predetermined lens 109 of the first lens array 110 reaches the entire light-receiving surface 114 serving as an area, which should be illuminated (an effective area shown in FIG. 14(a)), via the lens 111 on the second lens array 112 corresponding to the lens 109. Then, similarly, light having passed through separate predetermined lens 109′ of the first lens array 110 reaches the entire light-receiving surface 114 serving as an area, which should be illuminated, via a lens 111′ corresponding to the lens 109′.
Next, it is considered to arrange another pair of light source images in order to make use of the gap between the pair of light source images in the peripheral part of the lens array 112 shown in FIG. 13. As shown in FIG. 14(b), the decentering of the lens 109′ is adjusted so as to cause a light beam having passed through the lens 109′ of the first lens array 110 to reach the lens 111 instead of reaching the lens 111′.
In other words, the decentering of the lens 109′ is adjusted so as to insert at least one light source image of a pair of light source images, which are condensed by the lens 109′ separate from the predetermine lens 109 on the lens array 110, between a pair of light source images condensed by the predetermined lens 109 of the lens array 110. Therefore, at this point, the lens 111, which is one aperture having one center of curvature, includes at least three light source images.
The center of curvature of the lens 111 in the second lens array 112 is set so as to irradiate a light beam having passed through the lens 109 of the first lens array 110 on the light-receiving surface 114 via the lens 111. Therefore, a light beam, which passes through the lens 109′ to reach the lens 111 having a correspondence relation with the lens 109, cannot reach the entire light-receiving surface 114 serving as an area which should be illuminated (effective area). In other words, the light beam reaches an ineffective area shown in FIG. 14(b). Due to such reasons, with the conventional design method and constitution of decentering the first lens array 110 such that a light source image formed by the lens 109′ separate from the predetermined lens 109 of the first lens array 110 is arranged in a gap of light source images formed by the predetermined lens, efficiency of use of the illumination device is declined on the contrary.
Note that the lenses included in the second lens array 112 in FIG. 14 and the lenses included in the second lens array 112 shown in FIG. 9 are shown in the figure in different numbers and shapes. However, this does not relate to the essence of the description.
The constitutions described in Japanese Patent Laid-Open No. 05-346557 and Japanese Patent No. 3301951 have the same problems as the above-described examples. Note that the entire disclosure of the above-described documents is incorporated herein by reference in its entirety.